The invention relates to a wide-band low-reflection attenuated delay line for traveling wave tubes, particularly for the amplification of millimeter waves, comprising a hollow guide provided with successive transverse walls defining line cells, each of which walls are provided with a central opening for the passage of the electron beam and, in addition, at least one coupling opening therein. Disposed in the individual line cells and having their longitudinal axes extending approximately parallel to the longitudinal axis of the delay line are respective elongated attenuating bodies. A delay line of this general construction is known from German Pat. No. 2,347,209.
In the achievement of an effective attenuation arrangement in connection with extremely high working frequencies, for example, in the mm wave range, considerable technological difficulties arise. The attenuation elements must be so formed, disposed and mounted that they develop a high specific attenuation effect while only slightly reflecting over the whole operating band, and, at the same time, must additionally provide sufficient dissipation of the heat losses arising during operation. The desired matching of the attenuation course proves to be especially critical. As a rule, in this connection, the attenuation effect of successive line cells heretofor was altered stepwise in accordance with a specific function which must be precisely maintained. Such a tapering of the attenuation requires an exact measurement and careful positioning of the individual, variously sized attenuation bodies or members. If such tapering is achieved by variation in the length of solid cylinders (See German Pat. No. 2,347,209) instead of, for example, by separation of variously sized sections along the cylinder generatrix, or for example, by the use of attenuating wedges, unquestionably, a decrease can be achieved in the production expense. However, accurate reproduction of the desired effective matching values from tube to tube is not easily achieved, which becomes of particular importance in series production and subsequent tube replacements.